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Chapter 14
Earth’s
Interior
Earth’s Interior
Interior Terms
• Crust
– Oceanic
– Continental
• Mantle
– Upper
– Transition
– Lower
• Core
– Outer
– Inner
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Peridotite
Eclogite
Spinel
Perovskite
Xenolith
Discontinuity
Phase Change
Tomography
Kimberlite
How do we know what
is inside the Earth?
• Seismology: Earthquake waves
Interior Terms
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Basalt
• Asthenosphere
Chondrule
• Lithosphere
Multi-anvil press
Diamond anvil cell
Convection
Magnetic reversal
Dynamo
Magnetic field
Earthquakes
• Earthquake Monitor
• http://www.iris.edu/seismon/bigmap/index.phtml
• Cosmochemistry: Meteorites
• Experiments: Laboratory synthesis
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Major Parts
• Ocean water 0.025% of mass
• Crust (Above the Moho) 0.5% of mass
– Oceanic (7 to 10 km of basalt & gabbro)
– Continental (30 to 60 km of granite)
• Mantle - Moho to 2900 km - Solid Rock
– 65% of total mass
– Upper (Moho to 410km) (Olivine + pyroxene)
– Transition Zone (410 -670 km) (Silicate Spinels)
– Lower 670 to 2900 km (Perovskite + periclase)
• Core (2900 to 6367km) 35% of mass
– Outer Core (Liquid Metal)
– Inner Core (Solid Metal)
Crust
• Oceanic Crust (Basalt and Gabbro)
– Thin (7 - 10 km)
– Dense (2.9 - 3.1 g/cm3)
– Young (< 250 my)
• Continental Crust (Granite + Diorite +
Seds)
– Thick (30 - 60 km)
– Light (2.7 - 2.8 g/cm3)
– Old (250 - 4000 my)
Mantle
• Upper Mantle (Moho to 410 km)
– Peridotite (Olivine + pyroxene)
– Eclogite (Pyroxene + Garnet)
• Transition Zone (410 - 670 km)
– Spinels and Spinelloids
• Lower Mantle (670 - 2900 km)
– MgSiO3 - Perovskite
– MgO - Periclase
How do we know what’s there?
• Seismology
– S-wave shadow
– P and S reflections and conversions
• Meteorites:
– Earth formed from primitive meteorites
• Xenoliths from kimberlites & basalts
• Experiments
Core
• Outer Core (2900 to 5150km)
– Molten iron metal (+ ~10% lighter
element)
– No S-wave transmission
• Inner Core (5150 - 6378 km)
– Solid Iron Metal
– May slowly rotate relative to
mantle
Seismology
• S-wave shadow
– No S-waves opposite-side
earthquakes
– Core (outer) must be molten
• P and S reflections
– Discontinuities at 410 and 670 km
– Phase Changes
• P and S travel time anomalies
– Tomography
– Hot and cold regions
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Seismology
P-waves
S-waves
Clicker Question
• What observation led to the
conclusion that the Earth has a liquid
outer core?
• A) Earth’s gravity field
• B) P-wave shadow
• C) S-wave shadow
• D) Seismic reflection from 660km
• E) Polar wandering
Clicker Question
• Why does the P-wave shadow
exist?
• A) Seismic refraction into the slower
outer core
• B) P-waves cannot pass the liquid
outer core
• C) Seismic reflection at the coremantle boundary
• D) Seismic reflection from 660km
• E) No earthquakes large enough
Velocity Structure and Earthquakes at N.
Tonga
(VanderHilst, Nature (1995)
Red = slow = hot
green = fast = cold
Clicker Question
• What observation led to the
conclusion that the Earth has a liquid
outer core?
• A) Earth’s gravity field
• B) P-wave shadow
• C) S-wave shadow
• D) Seismic reflection from 660km
• E) Polar wandering
Clicker Question
• Why does the P-wave shadow
exist?
• A) Seismic refraction into the
slower outer core
• B) P-waves cannot pass the liquid
outer core
• C) Seismic reflection at the coremantle boundary
• D) Seismic reflection from 660km
• E) No earthquakes large enough
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Xenoliths
Xenoliths
• Xenoliths are ‘strange rocks’
• Xenoliths are inclusions in
kimberlites and basalts
• Xenoliths provide natural high
pressure rocks.
– Kimberlites bring diamonds and other
rock samples from as deep as 670 km.
– Basalts are derived from the lithospheric
mantle
Xenoliths
Breaking Xenoliths at a Diamond
Mine in South Africa
Xenolith-Peridotite
Meteorites
• Meteorites tell us of Earth’s bulk
composition
– Chondrites are primitive
meteorites
– Earth is “chondritic”
• Composition is similar to sun
minus H, He and other volatiles.
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Meteorites
Meteorites
Clicker Question
Clicker Question
• How do we know that the core is
made of iron?
• How do we know that the core is
made of iron?
• A) Earth has a permanent magnetic field
and iron is ferromagnetic.
• B) Iron metal is abundant in meteorites and
has about the right density for the core.
• C) Iron metal is abundant in volcanic rocks
and has about the right density for the core.
• D) Iron metal is an electrical conductor
• E) Iron is highly compressible.
• A) Earth has a permanent magnetic field
and iron is ferromagnetic.
• B) Iron metal is abundant in meteorites and
has about the right density for the core.
• C) Iron metal is abundant in volcanic rocks
and has about the right density for the core.
• D) Iron metal is an electrical conductor
• E) Iron is highly compressible.
Experiments
• Multi-Anvil Press
– Synthesis experiments to 1000 km depth
– Samples 1-5 mm3
• Diamond Anvil Cell
– Spectroscopy
– Ultrasound
– X-ray diffraction
Multi-anvil
Press
5000 ton
(Bayerisches
Geoinstitut)
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Multi-anvil Press Sample
Assembly
Carbide cubes retain a lot of
strain
Multi-Anvil Press Octahedron
Multi-anvil Press Sample
Assembly
Multi-anvil Press
Octahedral Assembly:
After and Before
Diamond-anvil Cell
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Interior Terms
Interior Terms
Interior Terms
Interior Terms
Interior Terms
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Interior Terms
Mica Crystal with Quartz @ 5GPa
DAC on Diffractometer
Clicker Question
• The diamond anvil cell can
create pressure greater than
the center of the Earth in the
laboratory
• A) True
• B) False
Clicker Question
• The diamond anvil cell can
create pressure greater than
the center of the Earth in the
laboratory
• A) True
• B) False
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410km:
Olivine
Density 3.2
Olivine
410km:Olivine
Wadsleyite
Wadsleyite
3.5 g/cm3
525 km
Wadsleyite
Ringwoodite
Wadsleyite
Ringwoodite Crystal with Quartz
660 km
Ringwoodite
Density 3.6
Perovskite + MgO
4.2 g/cm3
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660 km
Ringwoodite
Tetrahedral Si
Mantle Density vs Depth
4800
Perovskite + MgO
Octahedral Si
4600
4400
4200
Lower Mantle
4000
3800
Transition Zone
3600
3400
Upper Mantle
3200
3000
0
Clicker Question
200
400
600
800
1000
1200
Clicker Question
• The Earth’s mantle is made of:
• The Earth’s mantle is made of:
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A) Solid silicate rock
B) Molten silicate magma
C) Solid iron metal
D) Molten iron metal
E) Olivine
Clicker Question
A) Solid silicate rock
B) Molten silicate magma
C) Solid iron metal
D) Molten iron metal
E) Olivine
Clicker Question
• The seismic discontinuity at 660
km is thought to be caused by?
• The seismic discontinuity at 660
km is thought to be caused by?
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• A) A change in crystal structure
A) A change in crystal structure
B) A compositional change to metal
C) Melting of silicates.
D) Magnetic reversal
E) A change to a gas phase
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B) A compositional change to metal
C) Melting of silicates.
D) Magnetic reversal
E) A change to a gas phase
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Convection in solid mantle
Convection in solid mantle
• Driven by U, Th, K decay
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(internal engine)
Moves about 2 cm/yr
Causes earthquakes
Moves plates
Splits and rejoins continents
One Cell or two?
Clicker Question
Clicker Question
• The Earth’s outer core is made of:
• The Earth’s outer core is made of:
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A) Solid silicate rock
B) Molten silicate magma
C) Solid iron metal
D) Molten iron metal
E) Olivine
A) Solid silicate rock
B) Molten silicate magma
C) Solid iron metal
D) Molten iron metal
E) Olivine
Magnetic Field
• Due to electrical currents from
Earth’s dynamo.
• Convection in liquid metal outer core.
• Convection is coupled to Earth’s
rotation.
• Field is subject to sporadic reversals.
– Last reversal was 30,000 years ago.
• Field holds ozone layer (UV shield) in
place.
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Magnetic
Field
Reversals
Clicker Question
Clicker Question
• The Earth’s magnetic field is caused
by:
• The Earth’s magnetic field is caused
by:
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• A) Permanent magnet in the inner core.
• B) Magnetic minerals in the rocks
• C) Convection currents in the upper mantle
A) Permanent magnet in the inner core.
B) Magnetic minerals in the rocks
C) Convection currents in the upper mantle
D) Convection in the liquid metal outer core
E) Solar wind dynamo
• D) Convection in the liquid metal outer
core
• E) Solar wind dynamo
Interior Terms
• Crust
– Oceanic
– Continental
• Mantle
– Upper
– Transition
– Lower
• Core
– Outer
– Inner
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Peridotite
Eclogite
Spinel
Perovskite
Xenolith
Discontinuity
Phase Change
Tomography
Kimberlite
Interior Terms
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Basalt
Chondrule
Multi-anvil press
Diamond anvil cell
Convection
Magnetic reversal
Dynamo
Magnetic field
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